Electronic oscillator-detector



Aug. 27, 1946. w, w, HA EN ETAL 2,406,370

ELECTRONIC OSCILLATOR-DETECTOR Filed July 8, 1958 5 Sheets-Sheet 1 27 INVENTORS Russ-LL H. VAR/AN WILLIAM IM HmvsE/v Filed July 8, 1938 5 Sheets-Sheet 2 FIG-Z N 5 x mm w n mVW H .M Em .SL w PW Aug. 27, 1946. w. w. HANSEN ETAL 2,

ELECTRONIC OSCILLATOR-DETECTOR Filed July 8, 1938 5 Sheets-Sheet 3 OJCILLATORJ el/ 6;:

E-63 [p [3 [ll I I OVER BUNCHED EXCITA TION OPERATING REG/0N OVERBUNCHED ORDINARY EXCITATION Exc/TBT/orv a V AMPLITUDE INVENTORS RUSSELL H. VAR/AN WILLIAM W HANSEN 3 l/ 3 5 6% E u w. w. HANSEN ETAL ELECTRONIC OSCILLATOR-DETECTOR Filed July 8, 1938 5 Sheets-Sheet 4 INVENTORS RUSSELL H. VA RMN WILL/AM 14/ HANSEN V RIA ATTORNE 1946' w. w. HANSEN ET AL 2,406,370

ELECTRONIC OSCILLATOR-DETECTOR Filed July 8, 1938 5 Sheets-Sheet 5 I l II ,II IIIIIIIIIIIIIIIIIIII III WM l

F ET 5 g9 INVENTOR. F?ussE1.LH. VA R/AN WILL/AM W. HANSEN Patented Aug. 27, 1946.

UNITED STATES PATENT OFFICE ELECTRONIC OSCILLATOR-DETECTOR William W. Hansen, Sigurd F. Varian, and Russell H. Varian, Stanford University, Califl, assignors to the board of trustees of the Leland Stanford Junior University, Stanford University, Calif.

Application July s. 1938, Serial No. 218,064

4 Claims. 1

This invention relates, generally, to the generation, modulation, detection, amplification, transmission and reception of electromagnetic energy, and the invention has reference, more particularly to a novel electronic oscillator-detector adapted for such uses and operating at frequencies of the order of 10 or more cycle per second. 1

This invention relates to the following copending patents and applications: Patent No. 2,190,712 for High efliciency resonant circui granted Feb. 20, 1940 to W. W. Hansen; Patent No. 2,242,275 for Electrical translating system and method" granted May 20, 1941 to R. H. Varian; application Serial No. 185,382 for Radio measurement of distances and velocities, filed Jan. 17, 1938 in the names of R. H. Varian and W. W. Hansen; Patent No. 2,272,165 for High frequency electrical apparatus granted Feb. 3, 1942 to R. H. Varian, W. W. Hansen and L. M. Applegate; and Patent No. 2,280,824 for Radio transmission and reception" granted April 28, 1942 to W. W. Hansen and R. H. Varian.

In the above copending patents and applications there are described a number of embodiments of related inventions which have come to be known by the names, rhumbatron," klystron, buncher, and catcher. These names are used in the present specification. They may be defined as follows: A rhumbatron is a resonant circuit characterized by an electromagnetic field bounded by a substantially closed conducting member, i. e., a cavity resonator, and in which energy is transferred to or from the electromagnetic field by inductive loops or capacitive elements in the field or by a beam of electrons projected through the field. A "klystr0n is an ultra high frequency electrical apparatus composed of one or more rhumbatrons, i. e., cavity resonators, excited and coupled by a beam of electrons projected through the fields contained in the resonators. A "buncher is the cavity resonator in a two-resonator "klystron nearest the emitter of the electron beam, in which the electrons are alternately accelerated and decelerated at the frequency of oscillation of the "klystron. A catcher is the cavity resonator in a twoor more-resonator klystron farthest from the emitter of the electron beam, in which energy of the bunched electron beam is converted into electromagnetic field energy.

The principal object of the present invention is to provide a novel electronic oscillator-detector adapted for generating, transmitting, receiving, and detecting high frequency signals.

Another object of the present invention is to produce a modulator for high frequency oscillations in which amplitude modulation is accomplished without frequency modulation.

A still further object of the invention is to produce methods and means for detecting objects at a distance by the transmission and reception of radio waves intercepted by such objects.

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings,

Fig. 1 is a diagrammatic representation of the present invention in a form of embodiment using two separate electron beams.

Fig. 2 is a schematic diagram of a form of the present invention having properties similar to those of Fig. 1, but with two concentric electron beams.

Fig. 3 is a schematic diagram of a form of the present invention employing two opposed electron beams.

Fig. 4 is a curve representing the performance of the apparatus of the present invention.

Fig. 5 is a sectional view of an amplifier apparatus according to this invention employed for detecting the presence of objects.

Fig. 6 is a fragmentary plan view of the structure of Fig. 5.

Fig. 7 illustrates the apparatus of Fig. 6 employed in connection with suitable reflectors for locating objects.

Fig. 8 is a view similar to Fig. '7 but illustrates a somewhat modified arrangement, and

Fig. 9 shows the application of the device of Fig. 6 to a burglar alarm system.

Similar characters of reference are used in all of the above figures to indicate corresponding parts.

Referring now to Fig. 1, the present invention will be explained in a form convenient both for construction and explanation. In Fig. 1 there are four resonant circuit members or cavity resonators l, 2, 3, and 4 of the type shown in copending Patent No. 2,242,249 for Electrical converter" granted May 20, 1941 to S. F. Varian and W. W. Hansen. Resonators I and 2 together with resonators 3 and 4 and their associated apparatus comprise two inter-coupled velocity grouped electronic circuit means the principles of operation of which are described in Patent No. 2,242,275. In the first unit comprising resonators l and 2 there is an electron emitter 5 such as an activated oxide surface heated by a filament 6. The emitter is connected with a resonator orcircuit member '2 has stronger battery 77 for accelerating the electrons from emitter 5 into the resonator system. Resonator l is provided with a pair of spaced grids 5 and and two coupling loops ii and 52. connected to'a coaxial transmission line is for Loop 5 i is.

coupling to resonator'2, and loop, i2 is used for coupling into resonator ti. Resonators. l and 2 are also shown provided with coupling loops is and ill and connected antennae ill" and 68".

' oscillations in it than has consequently radiation from resonator? is of bunching efiect and appears with greater'in- Openings 2t and 25 may be used with or in lieu of antennae m" and i 0'." for receiving and radiating energy. Resonator 2 has a pair of spaced grids M and i5, and two coupling loops as and H. Loop i6 is connected to coaxial line 83 for coupling into resonator i, and loop ii is used to couple resonator 2'to resonator 3.

On the exterior of reson'ator2 there is shown a novel detector arrangement which resembles in part the detector arrangement shown in application Serial No. 185,382 but which has certain advantages over that arrangement. In the present arrangement, two spaced grids 2| and 22 are placed near the grid I5 but at an angle wit respect to the latter. A plate 23 is placed near the grid 22 on the side opposite grid i5. A second plate 22 is placed as indicated about at right angles to the surface of grid I5. The surface of plate 24 is provided with fins 25 or other means for preventing secondary electron emission from plate 24. Plates 23 and 24 are connected to a push-pull transformer 26 which delivers its output to a telephone or other receiver 21. Between the emitter 5 and the grid 8 there is located a control grid 31 connected to an oscillator 39 of comparatively low frequency. Between resonators and 2 there is a tubular electrode 38 connected to a second low frequency oscillator 39'.

Resonators 3 and 4 are arranged similarly to resonators and 2', respectively. Resonator 3 has a pair of spaced grids 28 and 29 and a coupling loop 3|. An electron emitter 32 and a battery 33 correspond to similar elements of resonators I. Resonator 4 has spaced grids 34 and 35 and a coupling loop 36.

The system shown in Fig. 1 may be operated in either of two ways. The simpler way is to omit resonators 3 and 4 and to operate the rest of the apparatus as a complete system within itself. A second way is more complicated, and also includes the use of resonators 3 and 4 and their efiects. The operation taking place when omitting resonators 3 and 4 being the simpler, will now be described. In this operation of the system the electrons of the beam in passing through the grids 8 and 9 of input resonator l are alternately accelerated and decelerated as explained in Patent No. 2,242,275, As a result of the changes in velocities of the electrons of the beam they arrive at the grid 4 of output resonator 2 in groups or bunches distributed in time at the frequency of oscillation of the system. Energy is taken from the electrons by the alternating field of resonator 2 and this resonator is thereby excited to a state of oscillation. Energy of oscillation is transmitted from resonator 2 to resonator I through coupling loop l6, transmission line l3, and coupling loop Thus, the field of resonator [is maintained in a state of oscillation and the electron beam is accordingly acted upon and bunched.

Radiation from the fields of both resonators and 2 or from either one is possible. Likewise, energy can be received by either one. The

tensity at resonator 2 than a signal introduced directly into resonator 2. Inasmuch asreception is better performed by resonator l, and

' transmission better performed from resonator 2,

radiating elements such as either antenna ID or hole 29' or both are used in the resonator 2, and receiving elements, such as either antenna it or hole 20, or both, are used in resonator. 1.

Assuming that a modulated carrier frequency is received by resonator through either hole 2a or antenna l0", then the electrons of the beam travel through grids M and i5 of resonator 2 and encounter grids 2| and 22. The electrons emerging from grid i5 have varying velocities depending upon the strength of oscillation in the resonators and 2. Some of the electrons pass through grids 21 and 22 and hit plate 23. Other electrons (i. e. the slower ones) are refiected from grids 2| and 22 to plate 24. The two grids 2| and 22 are parallel and close together. A potential difference, with grid 22 negative, is established between grids 2| and 22 by the battery 30. The resultant field between grids 2| and 2'2 acts like a flat mirror insofar as the slower electrons leaving grid I5 are concerned. These electrons enter the field between grids 2| and 22 and their motion is opposed by this field and they are deflected toward plate 24. The faster electrons are deflected (or, more accurately, refracted) but they penetrate the field between grids 2| and 22 and hit plate 23.

The slower electrons are not able to penetrate the field between grids 2| and 22 and they bounce to the left as in ordinary optical reflection from grid 2| to hit plate 2'4. In the structure constituted by resonators and 2, all the electrons leaving the grid |5 have substantially the same velocity when the system is not oscillating. As the amplitude of oscillation increases, the electrons vary more in velocity, the extremes of velocity being greater for greater amplitudes of oscillation. The potential diifererence between grids 2| and 22 is adjusted either so that most of the electrons are reflected toward plate 24, or so that most of them are permitted to pass through to plate 23. The precise difference of potential between grids 2| and 22 giving the most sensitive or the most eiiicient detector action, as may be preferred, can be found by experimental adjustment of battery 30. The detector characteristic of this system is analogous to that found in ordinary vacuum tube circuits. Since practically all the electrons emerging from grid l5 eventually strike either plate 23 or plate 24, any increase in current reaching one of the plates is accompanied by a decrease in current reaching the other plate. Hence, the current produced by electrons reaching plate 23 is electrical degrees out of phase with the current produced by electrons reaching plate 24, and accordingly the currents from plates 23 and 24 are appropriate to the operation of any push-pull apparatus, such as transformer 26 and receiver 21, usually used with push-pull detectors. Hence, the received signal is heard at phone 21.

The grid 31 and the-tube 38 and the oscillators 5 is amplified by the every modulating cycle.

39 and 99' are used to control the operation of the system as by producing modulation or for starting and stopping oscillation. The actions of grids in the location of grid 91 and tubes in the location of the tube 38 have been described in Serial application No. 185,382 and No. 2,280,824. The action of these elements can be summarized by mentioning that an alternating voltage applied to grid 31 or to tube 38 accomplishes amplitude modulation with some frequency modulation.

Also, in the use of grid 31 and tube 38 if the voltage is made sufficiently high the oscillation of the system can be stopped during part of The frequency of oscillators 39 and 39' may be any desired up to about cycles per'second, or even more if the frequency of the circuit members I and 2 is higher than 10 or 10 cycles per second. Ordinarily, the frequencies of oscillators 39 and 39' will be well within the frequency range of ordinary triode oscillators. Either grid 31 or tube 38 or bothmay be used. Ordinarily only one will be required, although in some instances it will be convenient to use both operating at different frequencies.

The assemblage shown in the figure will operate as a simple klystron for transmission of radio waves or for the detection thereof or both. It will also operate as a modulated oscillatortransmitter or as a superregenerative receiver. In one specialized application of the system it is set up as a combined transmitter-detector. For best results the assemblage is placed in a suitable parabolic or other reflector, as described in application Serial No. 185,382. The system is adjusted for sensitivity in either of two modes of operation. Either the electron accelerating voltage of battery I is set so that the phase of arrival of electrons in the resonator 2 is such as to give maximum oscillation, and the coupling is then reduced by adjusting loops ii and i6 sufficiently so the oscillator will barely oscillate, or the electron accelerating voltage is set so that the phase of arrival of the bunches in the resonator 2 departs considerably from that which gives maximum oscillation, and the electron current or coupling li-IG or electron accelerating voltage is adjusted just to sustain oscillation. Experiments indicate that the latter mode of operation is the more sensitive. Under these conditions of oscillation, radiation leaving the system by way of antenna "1" or hole 20 can return by reflection from a distant object and enter resonator l. The returned radiation. will produce a field in resonator i' which may have any possible phase difference relative to the "bunching field therein. The returned radiation will be amplified by bunching in resonator I, "catching" in resonator 2, and feed-back into resonator I in a manner analogous to that in a regenerative detector. The amplified signal will combine with the steady oscillation of the system and it will add to or subtract from the steady oscillation depending on the phase of the received signal relative to the steady oscillation of the system. The observed result of the action of the system will be to receive at receiver 21 a signal of undulating intensity as the distance from resonator l to the outside reflector or object varies. The variation in distance will cause a corresponding variation in phase of the received signal.

In the operation'of the system as described above in which the adjustment is critically made, the reception of energy at the frequency of the transmitted energy, that is, the reception of energy transmitted and reflected back to the system, has the same effect as if the rate of energy loss were changed by any other cause. The eflect is the same as if the radiation resistance were changed, and insofar as an analysis of operation of the system is concerned, the reflector or outside object which returns radiation to the system is in effect part of the system. Accordingly, it is convenient to consider the combined effects of transmission and reception as if the variation in resultant detected signal were the effect of variation of radiation resistance,

In these methods of operation grid 31, and oscillators 39 and 39 are not used.

Another way of operating the system is to use tube 99 either grid 31 or tube 38 with one of their oscillators 39 or 39' adjusted so that during part of the low frequency oscillation cycle of oscillators 39 or 39' the system will oscillate strongly and during another part of the cycle the same will oscillate weakly. It is characteristic of klystrons that they are comparatively sensitive to the effects of incoming signals when they are oscillating weakly but relatively insnsitlve when oscillating strongly. For effective radiation strong oscillations are desired. The adjustment of voltage on grid 31 or tube 38, whichever is used, is such as may be required to nearly stop oscillations during part of each low frequency cycle. During other parts of the cycle the system can operate with less restriction and at some parts of the cycle without any restriction.

Thus, the system transmits pulses of high frequency radiation, the pulses being at the repetition frequency of the low frequency oscillators 39 or 39', and in between pulses of radiation the system is prepared to receive radiation. If the transmitted radiation .encounters a suitable refiecting body or object some radiation will be returned to the system where it will be received and detected during the reception part of the low frequency cycle. In this mode of operation, the system operates alternately as a detector'and as an oscillator. Furthermore, it may operate as a superregenerative detector if adjusted properly. The conditions for superregeneration are, in general, fulfilled if the oscillator is allowed repeatedly to build up self-sustained oscillations for a period shorter than the time required for the oscillator to reach full oscillation, and then is stopped. The amplitude reached before oscillation is stopped is then sensitive to incoming signals.

Thus, it will be evident by reference to Serial No. 185,382 that the system described herein is applicable to the uses described in that application. In general, the present invention can be used in many applications such as location of remote objects requiring an oscillator-transmitter and receiver-detector operating either simultaneously or alternately. When using this apparatus for the purpose of locating remote objects a shield 4' would ordinarily be used between the transmitter antenna IO" and the receiver antenna "1".

The operation of the system shown in Fig. 1 including use of resonators 3 and 4 resembles that described when using resonators l and 2 alone, but the use of resonators 3 and 4 provides a novel type of control for resonators l and 2. This novel type of control accomplishes, in eflect, feed-back from resonator 2 to resonator l which is non-linear, that is, feed-back in which the transfer of energy is not proportional to the energy in the primary circuit. The use of this type For sensitivity in detection as an osclllator-de-' tector the mutual conductance. of the circuit should be substantially constant. The mutual conductance is the ratio of the change in output load current of the system to the change in input control voltage of the system. In the ordinary klystron, the mutual conductance is constant at small amplitudes ofoscillation, and then gradually decreases at large amplitudes of oscillation. This is indicated in Fig. 4 in whichthe mutual conductance of a circuit is indicated as ordinates and the amplitude of oscillation as abscissae. In this figure there are three curves drawn, one showing mutual conductance as a function of'amplitude in a klystron with ordinary or normal excitation, a second curve showing mutual conductance as a function of amphtude in a klystron with over-bunched" excitation, and a third curve showing the operation of a klystron with a combination of normal feedback and feed-back through an over-bunched klystron. In the curve showing operation with this combined form of excitation conforming to Fig. 1 when resonators 3 and 4 are used, there is a region in which the mutual conductance is substantially constant over a considerable range of amplitudes. This is indicated on the curve by the expression operating region.

For quantitative examination of the operation have a large relative change of amplitude with the klystron operating at small amplitude of oscillation or we now have a small relative change of amplitude with the klystron operat= ing at large amplitude of oscillation. present invention there are means for producing both a large amplitude of oscillation of the 1:13;- stron and a large'proportionate change in amplitude as'a function of radiation resistance at one and the same time. Under special conditions as represented in Fig. 4 by the curve marked over-bunched excitation, the mutual conductance can either decrease or increase with change in'amplitude depending on the degree of bunching. These conditions are produced in the arrangement shown in Fig. 1.

Resonators i and 2 and the elements associated with them are operated as described before substantially like an ordinary klystron. Resonators sand 4 operate substantially like an ordinary klystron except that the amplitude of oscillation in resonator 3 is greater than is usual of the klystron an expression for mutual conductance (Gm) is stated as follows:

Any convenient consistent system of units can be used in the above expressions.

For small values of a: in an ordinary klystron,

and as :c (or the input voltage V1) increases, Gm decreases, passing through zero and oscillating as indicated in Fig. 4. With variation of amplitudes of oscillation of resonator l, the mutual conductance varies according to an oscillating curve which is not constant for any appreciable part of its length except where a: is closeto zero.

It is only when operating with the mutual conductance very nearly constant that a small change in radiation resistance of the radiator can produce a large relative change in amplitude of oscillation, but if a large absolute change of amplitude-is desired, as well as a large relative change, the oscillator musthave a large ampli tude of oscillation. In the ordinary klystron," the mutual conductance is not constant when the amplitude of oscillation is la ge, hence we may in the buncher of a klystron. This is obtained by adjusting the coupling il-3i. That is, the amplitude of oscillation in resonator 3 is greater than the normal amplitude used in resonator i. The greater than usual amplitude of oscillation in resonator 3 produces a greater than usual alternating field between grids Z8 and 29. This field imparts larger than usual changes in velocity to the electrons drawn from emitter 32 through grids 28 and 29. The result is that the electrons after leaving grid 29 become bunched tothe optimum degree sooner in their transit toward grid 34 than they would with normal excitation, and by the time they reach grid 34 they have already passed through a condition in which they would extract energy from a, catcher circuit, and are progressing toward a second bunched condition in which they would deliver energy when they reach resonator 4.

Now in the curves of Fig. 4 if an amplitude of oscillation is selected in which the mutual conductance of the normal klystron l2 is decreasing, and the excitation of member 3 is adjusted so the mutual conductance at the same amplitude is increasing, anything that occurs in the system to change amplitude will cause the mutual conductance associated with the klystron l-2 and the electron beam thereof to change in the opposite way from the mutual conductance associated with the "klystron 34 and the electron beam thereof. That is. when the mutual conductance of resonators i and 2 increases, the mutual conductance of resonators 3 and 4 decreases and vice versa. The resultant effect is that over a portion of the operating range of amplitudes of the system, the mutual conductance of the system is substantially constant.

Under these conditions of operation the system can oscillate and radiate at a comparatively high power output, and at the same time be sensitively responsive to an incoming signal or to .a change in radiation resistance. In such a mode of operation the arrangement shown in Fig. 1 may be placed relative to a parabolic reflector as describedin Serial No. 185,382 with the antenna l0" connected to coupling loop I or the opening 20 facin the resonator at the resonator focus, or it may radiate without the aid of any other apparatus. If the transmitted beam goes out into uninterrupted space the system will oscillate and radiate stably. Suitable reflectors are also shown in Figs. 7 and 8 hereof.

I! while the system is radiating, a reflecting In the surface is placed to intercept the transmitted beam, some radiation may be reflected back into the resonator I either through coupling loop to or opening'w. This returned energy either adds to or subtracts from the energy in resonator I before and this correspondingly affects resonator 4 which finally reacts on resonator I through couplin 36-42. Referring again to Fig. 4, it will be seen that the increase of amplitude of oscillation in members and 2 results in a decrease of mutual conductance, whereas the increase of amplitude in members 3 and 4 results in an increase of mutual conductance. The combined effect of these changes is to retain for the system av substantially unchanged mutual conductance over a limited zone as indicated by the substantially horizontal portion of the curve shown in dash lines.

This system under the conditions described is, in the region specified, stably sensitive to received radiation, to which it responds depending on the magnitude and phase of the received signals. The responses of the apparatus to the received signal are detected, in the electron beam emerging from grid l5, by the elements numbered 2| to 21 inclusive. The particular arrangement for detection shown in Fig. 1 is only one of several that can be used. Other detection arrangements have been disclosed in application Serial No. 185,382 and Patent Nos. 2,272,165 and 2,280,- 824. The' subject matter of Fig. 1 is claimed broadly and specifically in our divisional application Serial No. 516,012 filed Doc. 29, 1943.

The general principles involved in the operation of the embodiment of this invention shown in Fig. 1 are applied also in a second embodiment shown in Fig. 2. In Fig. 2 only two resonators and 2 are employed. Resonators I and 2' have the same grids, coupling loops, and other appurtenances as in the structure of Fig. 1 except those associated also with resonators 3 and 4 of that figure, which of course are not required. In Fig. 2 two electron emitters 5 and 41 are used. Emitter 5 is similar to the corresponding emitter of Fig. 1, but is made somewhat smaller in proportion to the size of grids 8 and 9. Emitter 4| is of annular form concentric with and surrounding emitter 5. Two grids 42 and. 43 are provided in front of emitter 5 for the control of the shape of the field in the immediate vicinity of emitter 5. Two other grids 44 and 45 are provided at the adjacent surfaces, as shown, of resonators I and 2'. Grid 44 is connected to resonator I' while grid 45 is insulated from resonator 2' although supported thereon. Grids 42 and 43 are connected to emitter 4| and are maintained at a potential which is positive with respect to emitter 5. Grid 45 is positive with respect to emitter 5 and negative with respect to emitter 4|.

In the operation of the structure of Fig. 2, electrons from emitter 5 are formed as a cylindrical beam 45 projected along the axis of the system. This beam of electrons passes through resonators and 2' as usual in the klystron, providing excitation for resonator 2' feeding back through interconnected loops I6 and II to resonator I. Electrons from emitter 4| are formed as a beam 41 of annular cross section surrounding beam 48 and coaxial therewith. The electrons of beam 41 pass through resonator l' and are bunched as usual, but they do not enter resonator 2'. Instead they are reversed in transit between V grids 44 and 45 by the action of the latter grid,

and they are projected back through grids 9 and 8. The reversal of the electrons of beam 41 between grids 44 and 45 is, of course,'the consequence of having grid 45 negative with respect to the emitter 4|. The reversal of the electrons of beam 41 is illustrated in Fig. 2 by the doubling back of the boundary lines 48 of beam 41. These electrons of beam 41 are acted upon for bunching by resonator I when they pass initially through grids 8 and 9 in their travel toward grid 44, and the bunching process continues during the time the electrons, travel from grid 9 through grid 44 toward grid 45 and then back to grid 9. The energy of the bunched electrons of beam 4? acts upon the field resonator of I, these electrons being in an overbunched condition such that the mutual conductance contributed by this beam is increasing with increasing amplitude.

The operation of Fig. 2 in combined transmission and reception is similar to that of Fig. 1 as explained before with reference to Fig. 4. The characteristic of ordinary excitation shown in Fig. 4 is obtained by the action of the beam 46 from the emitter 5, and the characteristic of over-bunched excitation is obtained by the action of the beam 41 from the emitter 4|. The combined action of these two beams gives the combined excitation characteristic shown in dash lines in Fig. 4, i. e. a region in which the mutual conductance changes but little over a definite range of amplitudes. Accordingly, Fig. 2 can be used for those operations requiring simultaneous transmission and reception of signals as described for Fig. 1, in which case the shield 4' or equivalent is employed. In Fig. 2 the elements 2| to 21 inclusive shown in Fig. 1 for signal detection have been omitted for convenience, although they would be used in the same way in Fig. 2 as in Fig. 1.

The subject matter of Fig. 2 is claimed specifically in our divisional application Serial No. 463,290 filed Oct. 24, 1942.

Another arrangement capable of operating in a manner similar to that described for Figs. 1 and 2 is shown in Fig. 3. In this figure there are also disclosed elements for accomplishing additional functions. In Fig. 3, three resonators H, 12, and I3 are shown mutually spaced and centered on the same axis. Resonators H and 12 perform the functions of resonators I and 2' in Fig. 1 and resonators I2 and I3 perform the functions of resonators 3 and 4 in Fig. 1. A beam of electrons is projected from an emitter 5 through resonators II and I2, and another beam of electrons is projected from a second emitter 32 through resonators l3 and 12.

A third beam of electrons is produced by a third electron emitter 5| which projects this beam through the resonator 12 transversely of the axis of the system. This beam of electrons is admitted to resonator 12 through a grid 52 in the wall thereof. The beam passes between the faces containing grids l4 and I5, and it leaves resonator 12 through a grid 53. The electron beam after emerging from grid 53 is intercepted by a plate 54 in which there is an opening 55, and the part of the electron beam that goes through the opening 55 impinges on a plate 23,

Between the emitters 5 and 32 and their respective adjacent resonators H and I3 are control grids 51 and 58 connected to oscillators BI and 62 respectively. Coaxial with the system are located two conducting tubes 63 and 64 between resonators H and 12 and between resonators l2 and 13, respectively. Tubes 63 and 64 are connected to the respective ends of a. center-tapped secondary coil 65 of a transformer 66.

This arrangement shown in Fig. 3 can be operated in several ways. One method of operation corresponds closely to that of Fig. 2. The beam of electrons from emitter operates like the central electron beam of Fig. 2, and the beam of electrons from the emitter 32 operates like the outer electron beam of Fig. 2 which produces non-linear feed-back of energy into the resonator 12. The operation of the two systems with reference to Fig. 4 is the same.

In Fig. 3 the physical arrangement is such that the detector shown in Fig. 1 is not so convenient to use, and the transverse electron beam through resonator i2 is used instead. The operation of the transverse beam in detection is in accordance with principles disclosed in Patent No. 2,272,165, wherein it is disclosed that the electron beam is deflected vertically with respect to horizontal grids l4 and I5 by the alternating electric field between grids l4 and Hi. The deflection of the electron beam is a function of the amplitude of oscillation in the resonator i2, and the detected signal received from plate 23 by the receiver 21 is also a function of the same amplitude. The plate 5! can be arranged with reference to the transverse electron beam so that with no oscillation in resonator 12 substantially the entire cross section of the electron beam will pass through opening 55, or so that practically none of the beam goes through. In either case, oscillation developed in resonator 12 will cause a varia tion in the number of electrons passing through opening 55, the variation in the number of the electrons being a roportional or other function of the amplitude.

A second way of operating and using the arrangement of Fig. 3 is as a modulating system whereby the system is momentarily set into strong oscillation for the purpose of transmitting a strong signal and then the system has its oscillations damped so that the same will act as a sensitive receiver of reflected waves. When thus operating, the coupling l'!3| is adjusted so that resonator i3 does not overbunch the electron stream but cooperates fully with resonator i l, the two vertical beams from emitters 5 and 32 being adjusted so as to be equal. A modulating voltage of any practical frequency is introduced at the transformer 66 and through coil 65 to the tubes 63 and 64. In the center-tapped connections shown, the tube 63 will increase in potential when tube 64 decreases and vice versa. The effect of a variations in voltage of tube 63 taken alone is to change the time of flight of electrons in their course from resonator H to resonator I2, and also causes the frequency of oscillation of resonator 12 to vary slightly, an effect which may be undesired. A corresponding and opposing eifect occurs as a result of variation of voltage of tube 64. In the complete arrangement of Fig. 3, the power of excitation of resonator 12 can be drawn equally from members H and 13. Also, the adjustment of the system can be modulated by voltage from coil 65, and the effects of frequency change due to changes in time of flight in tubes 63 and 64 is neutralized by the tendency to'increase frequency due to one direction of change of voltage in one tube and the tendency to decrease frequency due to the opposite direction of change in voltage in the other tube. That is, if the tube 53 is swung positive with a resultant tendency to increase frequency, the tube 64 will be swung negative and its tendency will be to reduce frequency. The net effect will be that the amplitude of oscillation in resonator 12 will 'be reduced without any change in frequency.

This type of modulator is readily adapted to practice of the present invention. for if the modulating voltage is great enough to stop oscillation during part of the cycle of the modulating frequency, we have the condition known in the art as superregeneration. As is well known, a superregenerative receiver is very sensitive to incoming waves during the time when an oscillating state is building up in the system, and, at the same time, the average amplitude of oscillation for radiative purposes may be moderately large;

A-third mode of operation of Fig. 3 is related to the operation of Fig. 1, and is explained with ref erence to Fig. 4. In this mode of operation, the system acts as a transmitter and as a receiver of radio signals. As explained before, the ordinary klystron is a sensitive detector when its amplitude of oscillation is small, but is less sensitive when the amplitude is large. Accordingly, it can operate either as a detector or as a transmitter satisfactorily by periodically shifting the amplitude from one magnitude to another. This is accomplished in Fig. 3 by the action of either one of oscillators 6| or 62. Either one or the other alone is sufllcient so if one is used the other may be omitted. Assuming the use of oscillator 62, for example, the electron beam from emitter 5 and the coupling of loops II and I6 between resonators H and 12 are adjusted so that without the assistance of the electron beam from emitter 32 the system oscillates weakly and acts as a sensitive detector. With the electron beam from emitter 32 added at every positive half cycle of oscillator 62, the system is adjusted so that it oscillates vigorously. Then, the oscillator 62 is arranged so that its frequency can be varied as desired as by adjusting knob 62', and so that it impresses a potential on grid 58 suificient to substantially stop the electron beam from emitter 32 during alternate half cycles of the frequency of oscillator 62.

In using the device as shown, trouble may be caused under some circumstances by the electrons that pass clear through the catcher resonator I2, and enter the buncher resonator\|l or resonator 13 opposite their point of origin. In many cases these electrons will have a more or less random distribution in .time, and should therefore cause little trouble, but in case they do make trouble, these electrons can be completely removed by setting the two beams from the two bunchers H and 13 at a slight angle with respect to each other, or by the use of magnetic or electrostatic deflecting fields in the spaces between the resonators.

The operation of the system then develops as follows: Energy is radiated by means of coupling loop l0 and the antenna IO connected thereto. The radiated energy goes away from theoscillator and if a reflecting surface such as a remote object, for example, an aircraft, is present at a practical distance from the system, some of the radiated energy is reflected back to the system. This reflected and returned energy enters resonator ll through antenna I0" and is detected by the transverse electron beam from emitter 5|,

13 in the receiver 21. In the use of this system the operation is substantially as described in Serial No. 185,382, in which separate detectors and transmitting oscillators are used. Apparatus made in accordance with Fig. 3 is suitable for the same use as separate transmitters and detectors, the difference being in the structural combination and the necessary modifications. In the use of oscillators and detectors intermittently started and stopped at constant frequency there are, as mentioned in Serial No. 185,382, alternate regions in the radiation field from which reflected signals vary from zero to maximum. To avoid dead spaces" in the observed field the interrupting frequency is frequency-modulated at a lower frequency by an additional oscillator M and 14' connected to modulate the frequency of oscillator 6i and 88. Arrangement for accomplishing this are shown in Serial No. 185,382.

The change in frequency which would ordinarily occur when the electron beam current through resonator 12 is changed may be avoided by making the time of flight of electrons in the beam from emitter 32 such that the electrons will arrive in resonator I2 slightly out of phase with the beam from emitter 5. This will cause the beam from emitter 32 to produce another and independent change of frequency when the beam from emitter 32 is started and stopped and which may be made either positive or negative and of considerable magnitude. This can be used to neutralize the change in frequency due to presence of an increased number of electrons in resonators I2 and 13.

A fourth way of operating the system shown in Fig. 3 is to use it as a superregenerative detector. This is accomplished by using one of the beams for stopping the oscillations normally produced by the other beam. For example, the beam from emitter 5 may be adjusted so that with the beam from emitter 32 cut ofi, oscillations build up rapidly. but with the beam from emitter 32 added the oscillations are abruptly stopped. This is accomplished by timing the beam from emitter 32 to enter resonator 12 in phase opposite to that of the beam from emitter 5. Oscillator 62 is adjusted to cut off the beam from emitter 32 each half cycle. This starts and stops oscillations each cycle as required for superregenerative operation,

In Figs. 1 to 3, if desired, only a single radiating means supplied from either the electrongrouping circuit or on the electron energy absorbing circuit may be used both as transmitter and receiver.

In Figs. 1, 2, and 3, the usual arrangements for enclosing the system in evacuated enclosures have been left out of the drawings for convenience as they will be readily understood with reference to the art generally and to the related copending applications and patents cited.

In Figs-5 and 6 there is shown a short wave amplifier I5 of moderately high gain employing hollow resonators 18 to 19 having slotted side walls and external adjustable tuning bands 80 for deforming the walls and providing three stages of amplification. An aperture M in resonator I9 serves as a radiator on the output end of the amplifier while an aperture 82 in resonator 18 serves to receive energy radiated from aperture ill and reflected back by some remote object such as an aircraft. A shield 83 serves to eliminate direct radiation from entering aperture 82 to start the system oscillating and this action is further i4 prevented, if desired, by adjusting the phase of the electromagnetic field in resonator 16 to outof-phase relation with respect to that in resonator I9.

Since neither of the apertures 8i and 82 are shielded from waves reflected from the aircraft orother object, the amplifier can be set into oscillation by regenerative action due to energy emanating from the output of the amplifier being reflected back to the input.

So long as the strength of the received reflected signal is great enough so that when amplified by the amplifier it produces an output signal which is greater than the primary signal that was responsible for the initial reflection, the amplifier will break into oscillation provided the reflecting object returns the radiation in proper phase. Thus, the amplifier will detect the presence of a remote object by breaking into oscillation as indicated by a meter 83 connected across the terminals of a thermocouple 85. This thermocouple is positioned adjacent resonator 19 for receiving the beam from emitter 86. When the system breaks into oscillation the energy of the electrons reaching the thermocouple 85 is appreciably reduced causing the thermocouple to cool somewhat, and the reading on meter 84 correspondingly drops, thereby indicating the presence of an object.

Obviously, for the amplifier to break into oscillation due to the presence of an object at a considerable distance, the gain in the amplifier 15 must be large. With the gain in the amplifier large it may be difiicult to produce sufilcient shielding at 83 to prevent oscillation, but as above pointed out this difliculty may be overcome by so phasing the input with-respect to the output that regeneration will not occur. Complete control of the phasing is obtainable by varying the accelerating potential through adjustment of potentiometer arm 81.

The general construction of the amplifier 15 has been illustrated in Patent No. 2,280,824 and consists of an evacuated columnar central portion for accommodating the electron stream emitted from emitter 86 which central portion has a series of annular glass seals thereby enabling the portions 01 the resonators I6, l1, l8 and 19 that are exterior of the seals to be non-evacuated. These exterior resonator portions are adapted to he slipped over the ends of the central columnar evacuated portion into desired place along the length thereof. It is intended that the central evacuated columnar portion of the device may be made of standard dimensions, thus enabling the external non-evacuated portions of the resonators to be made of various dimensions or sizes thereby obtaining a series of devices oi. difiering operating frequencies. This amplifier operates in the manner similar to an ordinary cascade amplifier, except that in the presence case there are no metallic couplings of high frequency between stages, the coupling being supplied by the electron beam itself. The high frequency signal introduced into resonator 18 causes this resonator to bunch the beams slightly due to the field set up therein. These partly formed bunches deliver energy to the second resonator 11 which will acquire a much stronger oscillating field than the first and will therefore produce a more pronounced bunching of electrons in the third resonator I8. This action repeats itself in each successive stage.

It can be shown that the mutual conductance 15 of a one stage klystron or velocity-grouped electronic amplifier is 'n'ni tions that occur while the electrons are in flight between the buncher and catcher, i is the current in the beam and V is voltage diflerence required to give the electrons of the beam their velocity. In a typical cascade amplifier with the resonators located close to one another n has the value of about 5. It is easily possible to obtain a transmission of electrons through the grids now used of 70% and to obtain a current of milliamperes passing out of the second resonator I1,indicating that the current within the resonator I1 was slightly more than 7 milliamperes. By using the above formula for mutual conductance and the observed value of interactance resistance of approximately 1,500,000 ohms for a klystron of 18 centimeter wave length a voltage gain is oba total voltage gain of about 16,000 or power gain of about 25x10". Hence, if

of the power lost per cycle in the last stage I9 is returned to th first stage I6 by reflection from the remote object, the device will oscillate with no regeneration other than that supplied by the reflection. In practice, the device can be made considerably more sensitive by allowing sufliicient regeneration so that the same is very near the point of oscillation without the existence of the reflection in question.

Figs. 7 and 8 show the device as set up in practice to detect the presence of an object that has moved into a region scanned by the device, scanning being provided by means of elevation hand wheel 88 and azimuth hand wheel 89 operating through suitable gearing for orienting the amplifier in azimuth and elevation. In Fig. 7 the opening 82 of resonator I5 is shown located substantially at the focus of a reflecting parabola 90, whereas the radiating hole BI is shown located substantially at the focus of a second adjoining reflecting parabola BI. meter 84, as before, shows by its indication when the apparatus is directed at a remote object, which, of course. may be entirely obscured, as by clouds or darkness. With the apparatus set up so as to keep watch on a particular area, and adjusted so as not to oscillate initially, then as soon as any object moves into the field viewed, the resultant phase of all the reflections previously existing is upset and the device will oscillate if the change of phase is in the right direction. If a relatively short wave length to which the device is well adapted is employed, no intruding object can move an appreciable distance without upsetting the phase in the right direction to start oscillations and cause meter 84 to indicate the presence of the object.

In Fig. 8 the parabolic reflectors 90' and SI are spaced further apart and are more complete as to form, thereby obtaining somewhat better action. Dipoles 92 and 93 are shown employed in this figure connected through transmission lines to resonators I9 and I6, respectively.

It will be understood that the device of this present invention is also suitable for use for indicating the presence of objects in the path of 16 conveyances such as ships,- and for other uses. For example, in Fig. 9 the device is shown adapted for use as an automatic burglar alarm, any movement of an object in the room 94 serving to set up the necessary reflection for causing the amplifier to oscillate, which results in the operation of a relay 95 controlling an alarm bell 98. In some instances it may be desirable to use an amplifier I60 between the output of the amplifier I5 and relay 95.

In the appended claims we use the expression velocity-grouped electronic circuit means for designating a klystron, i. e. briefly but accurately designating the combination of cavity resonators, an electron emitter, and other necessary parts as described in Patent No. 2,242,275. The use of the word klystron" herein has particular reference to the following combination: In Fig. 1, the combination of resonators I and 2 with the emitter 5, and the combination of resonators 3 and 4 with the emitter 32; in Fig. 2 the combination of resonators I and 2 with the emitter 5; and in Fig. 3 the combination of resonators I and 2 with the emitter 5, and the combination of resonators 2 and 3 with the emitter As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In apparatus of the kind described, a hollow internally resonant member, means for producing a beam of electrons, means for directing said beam of electrons through said hollow internally resonant member to efiect velocity grouping of the electrons of said beam, a second hollow internally resonant member, means for directing said electron grouped beam into said second hollow internally resonant member, a third internally resonant hollow member, means for directing a beam of electrons therethrough to eiiect velocity grouping of the electrons of such last named beam, and means for directing said last named electron grouped beam into said second internally resonant hollow member.

2. The method of determining the presence of oscillations in an electron beam oscillator having an energy absorbing field, and to determine the residual amount of energy ofja stream of electrons after passing through said energy absorbing field, which method comprises removing electrons from the oscillator after they have passed through the energy absorbing field, and measuring the residual amount of energy possessed by said electrons by allowing the same to strike a solid object and measuring the heat thereby generated.

3. In apparatus of the character described, means for producing a grouped electron stream, means for absorbing oscillatory electromagnetic energy from said grouped electron stream, means interposed between said means for producing a groupe delectron stream and said energy absorbing means for varying the timeof transit of electron groups therebetween for production of amplitude and frequency modulation of the output of said energy absorbing means, and additional means for producing amplitude and frequency modulation of the output of said energy absorbing means to cancel the frequency modulation of said first named modulation means, without com- 18 said resonant circuit but in diiferent proportions than that obtained by said means for changing said electron velocity, whereby one form of modulation is cancelled while leaving a residual of 5 the other form of modulation.

WILLIAM W. HANSEN. SIGURD F. VARIAN. RUSSELL H. VARIAN.

Certificate of Correction Patent 0. 2,406,370.

August 27, 1946.

WILLIAM W. HANSEN ET AL. It is hereby certified that errors appear in the printed specification of the above numbered patent requu'mg correction as follows: Column 6, line 65, for antenna 10" read antenna 10"; column 8, line 45, for member read resonator; column 9, line 40, for Dec. read Dec. column 10, line 21, for field resonator of read field of resonator;

column 13, line 18, for Arrangement presence read present; column 15, line 5 read Arrangements; column 14, line 62, for 0, for meter read Meter; column 16, line 67,

claim 3, for groupe delectron read grouped electron; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 23rd day of September, A. D. 1947.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

